1. Field of the Invention
The present invention relates to a disk apparatus for recording information, and more particularly, to a thermal assisted type magnetic recording apparatus in which the coercivity of a magnetic disk is locally reduced by a heat element for recording information in a high density, magnetic recording is performed using a write element in this position, and thereafter, the information is read from the magnetic disk using a read element.
2. Description of the Related Art
FIG. 3 is a top plan view of the inside of enclosure of a magnetic disk apparatus. FIG. 4 is a cross-sectional view of the magnetic disk apparatus. As shown in FIGS. 3 and 4, the magnetic disk apparatus has, as principal constituent elements, a head 30, a disk 31, a rotary actuator 13, a head amplifier 27, a package board 28 and the like. The disk 31, fixed to one rotary shaft, is rotate-driven by a spindle motor about a point A at a speed of 3000 to 15000 revolutions per minute. The head 30, fixed to an arm, is rotate-driven by the rotary actuator 13 about a point B, and is freely movable in a radial direction of the disk 31. As the rotary actuator is appropriate for downsizing of the mechanism, this type of actuator is employed in all the recently-released magnetic disk apparatuses. Further, the head 30 floats with a constant interval from the disk 31 by utilizing the air flow of the rotating disk 31. A servo circuit, an interface circuit, a hard disk controller (HDC) and the like, as well as a data decoder and a data encoder as signal processing circuits, are packaged on the package board 28.
The construction of the head 30 will be described with reference to FIGS. 5A and 5B. FIG. 5A shows a cross section of the head 30, and FIG. 5B, a bottom surface of the head 30. The head 30, provided on a slider 32, has a write element 53 to form a magnetic pattern on the disk, a read element 54 to convert magnetic information leaked from the magnetic pattern on the disk into an electric signal, and the slider 32 to support these elements with an air bearing on the disk 30. The write element 53, having a coil and a magnetic pole, generates a write magnetic field to the disk 12 by feeding a write current through the coil. Further, the read element 54, having a magnetoresistive sensor utilizing a magnetoresistive effect, performs a reading operation by a resistance change of the sensor as a current change or voltage change. Note that the write element and the read element are given as conventional elements, and the present invention is not limited to these elements.
The operations and functions of the respective parts of the magnetic disk apparatus will be described with reference to a block diagram of FIG. 6 (with reference to FIG. 2). Upon data writing, the interface circuit 19 (same function in both FIG. 2 and 6) receives digital data from the outside, then the data is amplified to a write current via a data encoder 62 (similar to data encoder 26 in FIG. 2) and a write amplifier 15 (same function in both FIGS. 2 and 6) as signal processing circuits, and the write current is inputted into the write element 53 of the head 30 and converted into a write magnetic field.
Upon data reading, the read element 54 of the head 30 converts a leak magnetic field generated from the disk 31 into an electric signal. The electric signal is amplified by a read amplifier 14 (same function in both FIGS. 2 and 6), inputted into a data decoder 20 (same function in both FIGS. 2 and 6) as a signal processing circuit and demodulated to the initial digital data. The digital data is sent by the interface circuit 19 to an external host machine. The head 30 can freely move in the disk radial direction by the rotary actuator 13 (same function in both FIGS. 2 and 6). To write and read a particular data track, a following operation must be accurately performed in a target radial position. The servo circuit 16, which controls the following operation, measures accurate relative positions of the head 30 and the disk 31 from servo information previously written on the disk 31, and controls the operation of the rotary actuator 13 via an amplifier 17 to move the rotary actuator. The hard disk controller (HDC) 65 generally controls these processings.
To increase the storage capacity of the magnetic disk apparatus, it is necessary to write a small magnetic pattern onto the magnetic disk. For stable existence of small magnetic pattern, the disk must have a high coercivity. To invert the direction of magnetization of a high-coercivity disk, the write element of the head must generate a high magnetic field. However, in a case where a write element with a narrow track width for the purpose of writing small magnetic pattern, the generated magnetic field is weaken. Thus, the limit of storage capacity is a problem.
To solve this problem, a thermal recording system has been proposed. This system utilizes the principle of a widely used magneto-optic disk. A magnetic field is applied to a comparatively wide area and a narrow area of the disk is heated, thereby a magnetic mark is formed in the heat area. For example, Japanese Published Unexamined Patent Application No. Hei 4-47512 (patent reference 1) discloses a technique of increasing a disk temperature using laser light and forming a mark within a laser-light irradiation range, and a technique of forming an arc read element on a slider for high-efficiency reading of a formed circular-arc mark. Further, Japanese Published Unexamined Patent Application No. Hei 11-96608 (patent reference 2) discloses a technique of forming a mark, using a heat element with a resistor, within a resistor heating range, and a technique of forming a slider holding the resistor. Further, PCT/WO01/65547 (patent reference 3) discloses a technique of forming a circular-arc mark by increasing a disk temperature using laser light and performing following by offsetting a track position in correspondence with a change of yaw angle of a slider for the purpose of high-efficiency reading of the circular-arc mark.
However, in these techniques, as the write mark is determined based on the size of heat area, a comparatively large spot diameter of the laser light and the size of heat element set an upper limit of recording density. Further, as a comparatively large write element is employed, coil switching time sets an upper limit of recording speed.
[Patent Reference 1]
Japanese Published Unexamined Patent Application No. Hei 4-47512
[Patent Reference 2]
Patent Japanese Published Unexamined Patent Application No. Hei 11-96608
[Patent Reference 3]
PCT/WO01/65547
To solve these problems, a thermal assisted type magnetic recording system has been proposed. In this system, the temperature of an area of the disk is increased by a heat element, so as to reduce the coercivity of this area, and a magnetic pattern is formed using a write element in this coercivity-lowered area. This series of operations reduces a necessary magnetic field generated by the write element. Further, as the disk temperature changes back into a room temperature after the writing operation, even a small magnetic pattern can be protected from a thermal decay effect, and a write pattern can stably exist for long hours. The difference of the thermal assisted type system from the conventional thermal recording system is that in the thermal assisted type system, a magnetic pattern is formed in an area of magnetic field generated by the write element, whereas in the thermal recording system, a magnetic pattern is formed in an area heated by the heat element. In the thermal assisted type system, since it is possible to combine a disk with a high coercivity and a small write element, the storage capacity of the magnetic disk apparatus can be greatly increased.
However, the thermal assisted type recording system has a problem of change of yaw angle of the head accompanying the moving operation of the head along an arc in the disk radial direction using the rotary actuator. FIG. 7 shows an example where a center line of a heat element 72 and that of a write element 74 are shifted from each other upon occurrence of yaw angle in a head 71. Unless writing is performed by the write element within 10 microseconds after heating an area of the disk by the heat element 72, the heat area is spread and the temperature is lowered. Accordingly, this period should be preferably short. Further, writing cannot be performed after 4 to 20 milliseconds of 1 rotation of the disk. Accordingly, the heat element 72 and the write element 74 must be arranged on a straight line in a writing target track. In this example, as the yaw angle exists, the heat element 72 heats a track different from that where writing is made by the write element 74, accordingly, a magnetic pattern cannot be accurately formed on the disk. Note that as the reading operation is performed separately from the writing operation, a read element 73 regarding the reading operation does not set a limitation of a relative position to the heat element 72 and the write element 74. Further, in the above-described conventional thermal recording system, as a writing magnetic field is applied to a comparatively wide range, there is no problem regarding strict relative relations of the heat element 72 and the write element 74.
To solve the above problem, an apparatus structure with a constant yaw angle using a linear actuator must be adopted, otherwise, the area heated by the heat element and the area for the magnetic field generated by the write element must be brought into correspondence. However, as the liner actuator has a low rigidity, the accuracy of head positioning is lowered, and further, the linear actuator is a large and high-cost device. On the other hand, several techniques of bringing a heat area and magnetic-filed applied area close to each other are disclosed. For example, Japanese Published Unexamined Patent Application No. 2001-319387 discloses a technique of heating a position immediately below the write element by emitting laser light as heat means in a slanting direction by the side of the write element. In this technique, the problem of yaw angle can be mitigated, however, in a case where the interval between the head and the disk is reduced for writing a smaller magnetic pattern onto the magnetic disk, the effect of slanted emission of laser light is reduced and a position immediately below the write element cannot be heated. Further, Japanese Published Unexamined Patent Application No. 2002-50012 discloses a technique of embedding a waveguide in a position very close to the write element and heating a position around the write element by passing laser light through the waveguide. Also in this technique, the problem of yaw angle can be mitigated, however, in a case where the size of the write element is reduced for writing a smaller magnetic pattern onto the magnetic disk, formation of the waveguide is extremely difficult.